Method of preparing monomeric organotin dialkoxides



United States PatentOfiFice METHOD OF PREPARING MONOMERIC ORGANO- TIN DIALKOXIDES Gerry P. Mack, Jackson Heights, and Emery Parker, New

No Drawing. Application July 12, 1950, Serial N0. 173,478

7 Claims. (Cl. 260429) The invention relates to a method of preparing organotin dialkoxides or dialcoholates of the general formula R2Sn(0l )z wherein R stands for an alkyl or aryl group and R for an alkyl, aralkyl, or alicyclic group.

The known methods for preparing these compounds give very poor yields and the obtained products contain large amounts of organo-tin oxide and/or halide.

in our copending application, Serial No. 29,935, filed May 28, 1948, of which this application is a continuation-in-part, we have described a method for preparing organo-tin dialkoxides which consists in reacting an organo-tin halide in an anhydrous organic solvent with an alcoholate or with alcohol in the presence of an alkali metal, ammonia or a tertiary amine, removing the precipitated halide and distilling off the solvent under reduced pressure at temperatures not exceeding 150 C. In this way a product is obtained which consists of a mixture of monomeric and polymeric d1- alkoxides, the proportion of polymeric dialkoxides increasing with increasing temperatures and prolonged periods of heating. The polymeric and monomeric dialkoxides can be separated by treating the mixture with a lower alcohol, in which only the monomeric compounds are soluble.

It is a principal object of this invention to improve the process described in said prior application and to provide a method which readily produces from organotin halides in good yields directly monomeric organotin dialkoxides which are substantially free of halogen and polymers.

Other objects and advantages will be apparent from a consideration of the specification and claims. The improvement over 'themethod described in our 'copending application, Serial No. 29,935, consists in carrying out the reaction between organo-tin dihalides and lower aliphatic alcohols with completely anhydrous reactantsat temperatures below C., preferably 05 C., in carefully dried equipment and in distilling oil? the solvent under reduced pressure under rigorous exclusion of moisture, whereby also the access of air or oxygen should preferably be avoided. In this way, it is postible to obtain substantially halogen-free organo-tin dialcoholates of alcohols containing not more than 4 C atoms directly in the monomeric state in high yields.

a The reactions referred to hereinbeforemay be rep,- resented by the following equations:

the residue of an aliphatic alcohol having not more than 4 C atoms and Me is an alkali metal. As stated hereinbefore, the ammonia in.Equation 2 may be replaced Such amines are, for instance, trimethylamine, triethylamine, tributylamine, dimethylaniline, pyridine, N-methylmorpholine, and others. However, we prefer Reaction 1 to Reaction 2 because by a tertiary amine.

of the insolubility of the alkali halide in the organic solvent, .which. facilitates the removal of the halogen.

Examples of dialkyl and diaryl tin dihalides which may be employed in making the dialkoxides include the following: dimethyl, diethyl, dipropyl, dibutyl, dihexyl, dioctyl, dilauryl, others.

In the same way the corresponding dibromides may ,beused. j

As alcohols for the preparation of the dialkoxides,

diphonyl, dibenzyl tin dichloride, and

resins.

e. g. tetrahydrofurfuryloleate.

we can use saturated or unsaturated straight or branched chain lower primary, secondary, or tertiary aliphatic alcohols, such as: methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, isopropyl alcohol, sec. and tert. butyl alcohol, allyl alcohol, methallyl alcohol, and others.

We can use also other alcohols and thioether alcohols, such as methoxy ethanol, hydroxy ethyl methyl sulfide, and others. I

\Vhenever possible, we dissolve the organo-tin dihalides in the same alcohol with which they are subsequently brought to reaction and we carry out the reaction in the anhydrous alcohol which is to form the alkoxy groups of the tin compound. In this 'Way, only a single distillation step is necessary to obtain the pure dialcoholate; this is important because any rise of temperature such as is necessary for distilling on a solvent tends to polymerize the monomeric dialcoholates which are very unstable compounds; therefore, the reaction mixture and reaction products should be subjected to as few distillation steps as possible.

As the presence of water is objectionable in the preparation of the monomeric organo-tindialkoxides,' the intermediate alkali alcoholates should be prepared by methods in which no water is formed, or if formed, can be completely eliminated. Therefore, we prefer to use metallic sodium, or potassium, or sodium hydride in the preparation of alcoholates from the water soluble or low boiling alcohols.

In order to obtain products which contain no halogen or only traces of halogen, it seems to be necessary to prevent the organo-tin halide from contacting alkali metal but to react it only with the alkali alcoholate solution. ,7

The halogen-free monomeric organo-tin dialcoholates obtained according to the invention are valuable intermediates for the preparation of other organo-tin compounds and they offer a very convenient way to introduce the dialkyl or diaryl tin radical into organic compounds. They may be also converted into polystannanediol ethers by subjecting them to elevated temperatures in the presence of water vapor. When, for instance, in a vacuum distillation of a monomeric organo-tin dialkoxide, the pressure is regulated as usual by letting air in through a capillary tube, and when said air is saturated with moisture, the monomer is very quickly converted to the polymer according to the equation:

and only the respective alcohol and a negligible amount of the monomer are distilled off. i

It has been suggested to use monomeric organo-tin dialcoholates as stabilizers for resin compositions containing vinyl chloride units and for other halogen-cohtaining resins, though they present for this purpose serious drawbacks in view of their instability and because of their extreme sensitivity to moisture.

We have found a convenient way to handle and store such organo-tin dialkoxides, which method is particularly suited for admixing the monomeric dialkoxides with Thismethod consists in dissolving the dialkoxides in high boiling esters or hydrocarbons which are useful of themselves as plasticizers in the compounding of the resins, such as phthalates, like dioctylphthalate and similar compounds, adipates, sebacates, or organic esters of glycols, phosphoric acid, tetrahydrofurfurol, Said solutions may then be readily added to the resin mix.

The preparation of monomeric organo-tin dialkoxides according to the invention is illustrated but not limited by the following examples.

Example I I perature below 5 (3.- After the addition was completed,

stirring was continued until'the batch proved on titration to be neutral. The precipitate-was filtered otf and the .3 methanol distilled off -und '1' reduced pressure at at temperature of about 40 C. During all phases of the preparation, dry nitrogen was bubbled through the mixture.

, In this way, almostpure monomeric dibutyl dimethoxide was obtained in 92I7- yield, It contained 40.8% {(3,8;55% H, -39'.93% sn,:i20.-9 ethoxyandndchlorine. The "boilingpointwas "136%1 39 *C. at 1 .2 'min., the moleciilar weight in carnphor3'32, the-specific gravity at 20 C. 12862 and the refractive index at 20 'C. 1.4831.

"A water-clear colorless dibutyl tin dimethoxide'h'avin'g only traces of chlorine and the samephysical characteristics as'the compound described above was obtained also when the reaction was carried out at a temperature of about 50 'C. I

Example 2 9.2g. of sodium we're dissolved in 200 cc. of absolute 'm'ethanol under coolingyand to the cooled solution'49.5 g. ofidiethyltin=dichloride were added-at -5 C. Theaprogless of the reaction was followed --by determining the alkalinity of the batch. 'After the solution became-neutral the "salt -formed in the reaction was filtered off and then *the methanol was distilled under 'reducedpressure. During -thedistillation of the methanol more-salt separated out which was filtered off. After allmethanolhad been distilled out at reduced pressure 'of'about 100 mm. Hg, a :li'quidtproduct was obtainedw-hich was fractionated and was found to b'oilat 125 C. 'at 3 pressure. During the entireprocess care was taken to prevent the access 'of hu'midity into the equipment used -for the'ipreparation.

The obtainedproduct was monomeric diethyl tin methoxi'cle and contained 49.61% Sn and 26.0% methoxy.

Example 3 18.4 g. of sodium metal were dissolved under cooling in 800 cc. of n-bu'tyl alcohol; 12116 g. of dibutyl'tin dichloride, dissolved in 200 cc. of -n-butyl alcohol, were "added to said clear sodium buto'xide solution at 0 C. with simultaneous introduction of dry nitrogen. The reaction mixture was carefully protected from moisture and the formed precipitate was allowed to settle to the bot tom of the reaction vessel; the supernatant solution was siphoned 05 under nitrogen pressure. After distilling off the butanol at 100 C. and L5 mm. Hg pressure, a clear liquid was obtained, the composition of which was very close to the formula (C4H)2SH(OC4H9)2. The product was stable only when well protected from moisture.

Example 4 v 18.4 .g. of sodium metal were dissolved in 400 cc. of absolute methanol 'and to the clear solution 99 g. of diethyl tin dichloride dissolved in 150 cc. of methanol were slowly dropped in. The temperature rose rapidly and was maintained by cooling at-20-30 C. The access of moisture was prohibited by protecting the reaction vessel with drying tubes. After the reaction mixture became neutral, thesalt was filtered oil and the methanol distilled under reduced pressure. The residue was a color-less 'oil obtained ina yield of 94% based on the theoretical yield. According to the analysis it had the formula CzHs OCH:

n CZEE/ corn and contained 49.83% Sn and 25.88% 'OCHs (required 49.72% Sn and 25.96% -OCHQ). The boiling point of the diethyl tin 'dirnethoxide was 1-2'4l26 C. at 3 mm. Hg pressure. At 20 C., it had the specific gravity of 1.4804 and a refractive index of 1.4206.

Example 5 9.2 g. of sodium metal were dissolved in 250 cc. of absolute methanol, 'andto the "clear solution a solution of 70 'g. of diphenyl tin dichloride inabsolu't'e methanol was added slowly under cooling. Afterthe reaction mixture became neutral, the salt formed .in the reaction was filtered ofi and the excess methanol distilled ofi under reduced pressure. The residue was a colorless sticky wax-like product which solidified on standing in the vacuum desiccator "to a white solid. The obtained product was diphen'y'l tin dimethoxide of the formula 4 and-contained 3 5.40% "of Sn"a11d"l--8:40% of-0CHs(t-heoretically 35.45% Sn and 18.52% OCHs). It had no melting point and decomposed on heating at 270 C.

Example 6 11.5 g. of sodium metal -were dissolved under cooling in 3 00 cc. of allyl 'alcoho. Toythe solution so obtained, a solution of 76.0 (g. ofdibutyl-tin dichloride in 70 cc. of allyl alcohol was added under strong stirring and cooling 910-5 C. Afterthe reaction was completei the s'odium 'chlo'rideformedin'thereaction "as filtered off, then the excess allyl alcohol was removed -unde'rreduced pressure at a temperature not exceeding 30 C. During all those operations'extreme "care -was take'n to avoid""a 'contact with moist air, which was "accomplishedby leading dry nitrogen gas through the reaction mixture and filtering the batch under nitrogen pressure. The remaining liquid product, after removing a small amount of sodium chloride which recipita'ted during vacuu aistiuauon, co'rresp'onaea to dibutyl tin dialloxide ofthe-formula The tin content =of-the compound was 36:38% (required 36.54%) and the allyl alcohol {content was 36.0% :(required 35.8%). T he compound was-easily soluble inorganic solvents but .it hydrolyzed "when exposed to moist air. and become insoluble-in cold alcohols.

'Fromthe foregoing examples, it will'be noted that -the tendency of the organ c-tin dialkoxidesto polymerize during their preparation-increases with increasing length'of the hydrocarbon chain of the'respective'a-lcohol. 'Wher'eas puremonom'eric organo tin methoxides can :bereadily obtained at temperaturesof about 50 *C.-, cooling totpr'o- -gress ively lower temperatures must be applied when the reaction :is carried out with alcohols =havi'n'g up to '4 C atoms. We have not been :able to obtain, in the manner'described, directly ipure monomeric dialkoxides of alcohols having more than 4 C atoms. Similarly, except'in the case of methanol, the removal of the unreacte'd alcoh'olhas to be carriedout under'reducedipressure at relatively low terrip'eratur es 'as quickly as possible in order to avoid "polyrneri'zation*during the distillation step.

Polymeric dialkyl and diaryl tin dialkoxid'e's and their preparation are claimed in our copending application, Serial No. 29,935, filed Ma'y 28, 1948. 4

Various modifications in "the =c0m'p'osition andin the preparation of the monomeric-organo tindialkoxides will be apparent to those skilled in the art andsueh modific'a- 'tions are included in the scope of 'the invention as 'defin'ed by the appendedclaims.

What we claim is:

1. A process for preparing substantially halogen-free compositions containing monomeric 'dialkyl "tin dialkox- -ides from dialkyl tin dihalides comprising the step's of'causing a dialkyl tin dihalide to re'actjunder anhydrous conditions at a temperature below 20 C. with substantially the s'toichio'metric amount of an alkali metal 'al'cohola te of an alcohol having not more than *4 C atoms, removing the precipitated alkali -h'alide, and distilling off the solvent at reduced pressure under completely dry conditions.

2. A process as defined in claim 4 wherein an alkali metal alc'oholate of a saturated-alcohol is employed.

3. A process 'as defined in claim 4 wherein an alkali metal alcoholate of an unsaturated "alcohol is employed.

'4. A process for'preparing "sub" 'anti'ally halogen-free monomeric dialkyl tin dialk'o'xides "comprising the steps of dissolving a dialk'yl tin jdihalide in an anhydrous alcohol containing not more than 4 carbon atoms, reacting "said solution at a temperature below 20 C. underexclusion 'of moisture with an 'alka'li'alcoholaitejof the alcohol used-as a solvent forthe dia'lkyl tin dihalide, frenioving the formed precipitates, and distilling [Off the unreacted alcohol in the presence of'a compeltely dry inert .gas under re'duced pressure. I p H 5. A process as defined in claim 4, 'where'inthedi'al'kyl tin dihalide and the alkali alcoholate are reacted withe'ach other iasubsrantianyeqniniblecular amounts.

'6. A process tor preparing substantially halogen free monomeric dialkyl tin dimetho'xide comprising "the steps of dissolving a dialkyl tin dihalide in anhydrous methanol,

reacting said solution under anhydrous conditions at a temperature below 20 C. with alkali methylate, removing the precipitated alkali halide and distilling off the unreacted methanol in the inert gas.

7. A process for preparing monomeric dibutyl tin dimethoxide substantially free of chloride and dibutyl tin oxide comprising the steps of dissolving dibutyl tin dichloride in anhydrous methanol, reacting said solution under anhydrous conditions with alkali methylate at a temperature not exceeding about 5 C. so as to substantially prevent the formation of dibutyl tin oxide, removing the precipitated alkali chloride, and distilling ofi the unreacted methanol under reduced pressure in the presence presence of a completely dry 5 of a completely dry inert gas at a temperature not exceeding about 40 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,453,520 Langkammerer Nov. 9, 1948 2,476,833 Albert July 19, 1949 2,481,086 Cleverdon et al Sept. 6, 1949 2,484,508 Hill Oct. 11, 1949 2,489,518 Burt NOV. 29, 1949 OTHER REFERENCES Aronheim: Ann. der Chemie, vol. 194 (187 8). 

1. A PROCESS FOR PREPARING SUBSTANTIALLY HALOGEN-FREE COMPOSITIONS CONTAINING MONOMERIC DIALKYL TIN DIALKOXIDES FROM DIALKYL TIN DIHALIDES COMPRISING THE STEPS OF CAUSING A DIALKYL TIN DIHALIDE TO REACT UNDER ANHYDROUS CONDITIONS AT A TEMPERATURE BELOW 20*C. WITH SUBSTANTIALLY THE STOICHIOMETRIC AMOUNT OF AN ALKALI METAL ALCOHOLATE OF AN ALCOHOL HAVING NOT MORE THAN 4 C ATOMS, REMOVING THE PRECIPITATED ALKALI HALIDE, AND DISTILLING OFF THE SOLVENT AT REDUCED PERSSURE UNDER COMPLETELY DRY CONDITIONS. 